Zalaga

bbc micro/electron/atom/risc os coding queries and routines
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marcelaj1
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Zalaga

Post by marcelaj1 » Sat Sep 12, 2020 9:12 pm

Not sure where to post this ........

Playing around with my new working (thanks guys) Gotek stumbled upon Zalaga

On my beeb when I kill an alien it "explodes" but the explosion does not clear, in the screen shot you can see it behind the score sheet.
20200911_170620.jpg
Same ssd played on beebem no problem.

Searching this site there seem to be issues in the past with the game using 65C02 op codes, but my beeb has a 65C02, but the beebem setup I used was bog standard.

Any ideas?

cmorley
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Re: Zalaga

Post by cmorley » Sat Sep 12, 2020 9:16 pm

marcelaj1 wrote:
Sat Sep 12, 2020 9:12 pm
Searching this site there seem to be issues in the past with the game using 65C02 op codes, but my beeb has a 65C02, but the beebem setup I used was bog standard.
I think Zalaga uses 6502 illegal opcodes & therefore (unpatched) doesn't work on a 65C02. I believe it doesn't run on a Master for the same reason. Try changing beebem to a Master and see if you get the same problem.

tom_seddon
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Re: Zalaga

Post by tom_seddon » Sat Sep 12, 2020 11:39 pm

cmorley wrote:
Sat Sep 12, 2020 9:16 pm
marcelaj1 wrote:
Sat Sep 12, 2020 9:12 pm
Searching this site there seem to be issues in the past with the game using 65C02 op codes, but my beeb has a 65C02, but the beebem setup I used was bog standard.
I think Zalaga uses 6502 illegal opcodes & therefore (unpatched) doesn't work on a 65C02. I believe it doesn't run on a Master for the same reason. Try changing beebem to a Master and see if you get the same problem.
Apparently BeebEm's Master setup has some hacks to ensure this sort of thing runs as it might on a B, so I'm not sure I'd trust BeebEm to give an accurate indication of whether something should (or not) work on real hardware!

Play It Again Sam 10 apparently contains a 65c02-friendly of Zalaga, that I assume would work on Master and B (65c02 or not) alike.

--Tom

marcelaj1
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Re: Zalaga

Post by marcelaj1 » Sun Sep 13, 2020 2:29 pm

Ran the game in B and Master mode with no problem, so it must be something in my beeb causing it.

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tricky
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Re: Zalaga

Post by tricky » Sun Sep 13, 2020 3:33 pm

If you are using a master with an os switcher, that can confuse the game.
Well, if it is switched to mismatch the machine.

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richardtoohey
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Re: Zalaga

Post by richardtoohey » Mon Sep 14, 2020 4:43 am

I thought the illegal opcodes were more to do how the aliens were drawn, not so much to do with the explosions.

Have to go rummage around and see.

Do things like Planetoid and Snapper etc. work OK? I'm trying to think of games that tickle the 6522 - think Planetoid does that.

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